Certain products, particularly fluid products, must undergo heat treatments for partly or wholly destroying the microbial population, thereby extending the shelf life of the product, i.e. the time corresponding, under predetermined conditions, to an acceptable reduction of the organoleptic quality of a product.
Such treatments stabilize the microbial count for a time that depends on the specific type of treatment, i.e. essentially on the selected time-to-temperature ratio.
On the one hand, a higher temperature is more effective in destroying the microbial flora, on the other hand an excessively long treatment time would tend to degrade most of the nutrients in the product, thereby reducing its organoleptic qualities. Thus, treatment times and temperatures have to be mutually adjusted to meet the combined needs of obtaining a quality product with an adequate shelf life.
Conventional treatments, such as sterilization, pasteurization, cooking or the like, cannot fulfill this need. Treatments range from “mild” treatments (low temperatures and long treatment times), which keep the organoleptic properties of the product substantially unaltered but involve a very short shelf life, to “strong” treatments (high temperature and short treatment times), providing a long shelf life but an unacceptably low organoleptic quality.
In an attempt to overcome these drawbacks, apparatus have been provided which tend to minimize the microbial count in the product at relatively low temperatures.
U.S. Pat. No. 2,550,584 discloses an apparatus for heat treatment of milk, which comprises a duct of non-electrically material, for receiving milk from an external tank and conveying it, a radio-frequency voltage generator and an applicator device having a plurality of annular electrodes connected in use to an oscillator to generate a radio frequency electromagnetic field therebetween. Two of these electrodes are at the same electric potential, to generate electric and magnetic components in a preferential direction, i.e. parallel to the axis of the pipe.
One drawback of this known solution is that an electric current passes through the milk, thereby tending to degrade the most valuable nutrients of the product to be treated, such as vitamins and proteins. Therefore, the resulting product exhibits poorer organoleptic properties. Furthermore, the milk that is treated by means of this apparatus tends to turn darker, due to the Maillard reaction, followed by enzymatic browning, with a consequent degradation of the properties of the product.
A further drawback is the excessive power consumption required to obtain a proper treatment of the product, because the product is generally heated unevenly, and very long treatment times are required for even heating.
Uneven heating also tends to create areas, in the product, in which the induced electromagnetic field has a higher intensity, and in which the product is subjected to degradation, thus strongly jeopardizing the organoleptic quality as a whole.
Also, relatively low power can only be used with such known system, and this adversely affects treatment times, leading to the above mentioned consequences.
From EP-A-1198997 a pulse sterilization apparatus is known. However, this apparatus also does not solve the aforementioned problems insofar as during use an electric current can pass through the product to be treated, thereby tending to degrade the most valuable nutrients thereof.
Other food product treatment apparatus are known from U.S. Pat. No. 5,690,978, US-A-2001/13467, WO 03/101153, DE-A-4112383, DE-A-1010201, EP-A-1000554, U.S. Pat. No. 4,169,029, GB-A-598486.